1. Field
The present disclosure relates to a system and a method for using a common set of multi-purpose images for streak detection, color density, and color-to-color registration in an image printing system.
2. Description of Related Art
In various reproduction systems, including xerographic printing, the control and registration of the position of an image bearing surface, such as photoreceptor belts, intermediate transfer belts, or images thereon, is important. It is well known to provide various single or dual axes control systems, for adjusting or correcting the cross-process position or process position or timing of a photoreceptor belt or other image bearing surface of an image printing system, such as by belt lateral steering systems or belt drive motor controls. It is also known to adjust or correct the cross-process position or process position or timing of the placing of images on the image bearing surface with adjustable image generators such as laser beam scanners.
An important application of such accurate image position or registration systems is to accurately control the positions of different colors being printed on the same intermediate or final image substrate, to insure the positional accuracy (adjacency or overlapping) of the various colors being printed. That is not limited to xerographic printing systems. For example, precise registration control may be required over different ink jet printing heads or vacuum belt or other sheet transports in a plural color ink jet printer.
It is well known to provide, image registration systems for the correct and accurate alignment, relative to one another, on both axes (the cross-process direction axis or the process direction axis), of different plural color images on an initial imaging bearing surface member, such as (but not limited to) a photoreceptor belt of a xerographic color printer. These image registration systems improve the registration accuracy of such plural color images relative to one another or to the image bearing surface, so that the different color images may be correctly and precisely positioned relative to one another or superposed and combined for a composite or full color image. Further, these image registration systems provide for customer-acceptable color printing on a final image substrate such as a sheet of paper. The individual primary color images to be combined for a mixed or full color image are often referred to as the color separations.
Color registration systems for printing, as here, should not be confused with various color correction or calibration systems, involving various color space systems, conversions, or values, such as color intensity, density, hue, saturation, luminance, chrominance, or the like, as to which respective colors may, be controlled or adjusted. Color registration systems, such as that disclosed herein, relate to positional information and positional correction (shifting respective color images in the cross-process direction or in the process direction or providing image rotation or image magnification) so that different colors may be accurately superposed or interposed for customer-acceptable full color, intermixed color, or accurately adjacent color printed images. The human eye is particularly sensitive to small printed color misregistrations of one color relative to one another in superposed or closely adjacent images, which can cause highly visible color printing defects such as color bleeds, non-trappings (white spaces between colors), halos, ghost images, etc.
Known means to adjust the registration of the images on either or both axes relative to the image bearing surface and one another include adjusting the position or timing of the images being formed on the image bearing surface. That may be done by control of ROS (raster output scanner) laser beams or other known latent or visible image forming systems.
In particular, it is known to provide such imaging registration systems by means of marks-on-belt (MOB) systems, in which edge areas of the image bearing surface laterally outside of its normal imaging area are marked with registration positional marks, detectable by an optical sensor. For belt steering and motion registration systems (previously described) such registration marks can be permanent, such as by silk screen printing or otherwise permanent marks on the belt, such as belt apertures, which may be readily optically detectable. However, for image position control relative to other images on the belt, or the belt position, especially for color printing, these registration marks are printed and not permanent marks. Typically, they are distinctive marks printed with, and adjacent to, the respective image, and developed with the same toner or other developer material as is being used to develop the associated image, in positions corresponding to, but outside of, the image position. For example, the marks may be printed along the side of the image position or in the inter-image zone between the images for two consecutive prints. Such marks-on-belt (MOB) image position or registration indicia are thus typically repeatedly developed and erased in each rotation of the image bearing surface. It is normally undesirable, of course, for such registration marks to appear on the final prints (on the final image substrate).
In the marks-on-belt (MOB) system, the measurements are taken at two or more lateral or cross-process positions. This is because the marks-on-belt (MOB) sensors are fairly expensive. Therefore, it is desirable to eliminate the use of the marks-on-belt (MOB) sensors and have their function performed by other, less expensive and higher resolution means.
The present disclosure proposes a method and a system to measure the misregistration between the colors. The present disclosure uses a linear array sensor as a color registration sensor, and replaces the chevron ensembles that are used in the marks-on-belt (MOB) systems with a plurality of registration marks (e.g., corresponding to each color separation in a color model) on the image bearing surface.